TIRE WITH TREAD FOR LOW TEMPERATURE PERFORMANCE AND WET TRACTION

Abstract

This invention relates to a tire with a tread of a rubber composition that promotes a combination of winter traction at low temperatures and for promoting wet traction. The tread rubber composition contains a combination of low surface area silica and high softening point traction resin. Elastomers for the tread rubber composition are comprised of high cis 1,4-polybutadiene rubber and styrene/butadiene rubber.

Claims

1. A pneumatic tire having a circumferential rubber tread intended to be ground-contacting, where said tread is a rubber composition comprised of, based on parts by weight per 100 parts by weight elastomer (phr): (A) 100 phr of conjugated diene-based elastomers comprised of; (1) about 50 to about 10 phr of cis 1,4-polybutadiene rubber having a Tg in a range of from about −90° C. to about −110° C. and an isomeric cis 1,4-content of at least 95 percent, (2) about 50 to about 90 phr of styrene/butadiene elastomer having a Tg in a range of from about −65° C. to about −55° C.; (B) about 100 to about 200 phr of rubber reinforcing filler comprised of rubber reinforcing carbon black and precipitated silica where said precipitated silica has a nitrogen surface area of in a range of from about 50 to about 110 m.sup.2/g, wherein the rubber reinforcing carbon black is present in an amount of from about 2 to about 15 parts by weight per 100 parts by weight rubber, together with silica coupling agent for the precipitated silica having a moiety reactive with hydroxyl groups on said precipitated silica and another different moiety interactive with said diene-based elastomers; and (C) about 30 to about 70 phr of traction promoting resin comprised of at least one of styrene-alphamethylstyrene copolymer resin having a softening point in a range of from about 110° C. to about 130° C., terpene-phenol resin having a softening point in a range of from about 120° C. to about 170° C., coumarone-indene resins having a softening point in a range of from about 140° C. to about 150° C., petroleum hydrocarbon resins having a softening point in a range of from about 110° C. to about 170° C., and terpene polymer resins having a softening point in a range of from about 110° C. to about 170° C.; wherein said styrene/butadiene elastomer has a styrene content in a range of from about 10 to about 20 percent and a vinyl 1,2-content based on its polybutadiene portion in a range of from about 25 to about 35 percent, wherein said styrene/butadiene elastomer is an end-functionalized styrene/butadiene elastomer with functional groups reactive with hydroxyl groups on said precipitated silica comprised of alkoxy and at least one of primary amine and thiol groups, and wherein said silica coupling agent is comprised of bis(3-triethoxysilylpropyl) polysulfide containing an average in range of from about 2 to about 4 sulfur atoms in its polysulfide bridge.

2. The tire of claim 1 wherein said traction promoting resin is comprised of at least one of said styrene-alphamethylstyrene resin and terpene-phenol resin.

3. (canceled)

4. (canceled)

5. (canceled)

6. (canceled)

7. The tire of claim 1 wherein said styrene/butadiene elastomer is an end-functionalized styrene/butadiene elastomer with functional groups comprised of alkoxy and thiol groups.

8. The tire of claim 1 wherein said precipitated silica and silica coupling agent are pre-reacted to form a composite thereof prior to their addition to the rubber composition.

9. The tire of claim 1 wherein said precipitated silica and silica coupling agent are added to the rubber composition and reacted together in situ within the rubber composition.

10. (canceled)

11. (canceled)

12. The tire of claim 1 wherein said silica coupling agent is comprised of a bis(3-triethoxysilylpropyl) polysulfide containing an average of from about 2 to about 2.6 sulfur atoms in its polysulfidic bridge.

13. (canceled)

14. (canceled)

15. The tire of claim 1 wherein said traction promoting resin is said petroleum hydrocarbon resin.

16. The tire of claim 1 wherein said traction promoting resin is said terpene polymer resin.

17. (canceled)

18. (canceled)

19. The tire of claim 1 wherein said tread rubber composition is sulfur cured.

20. The tire of claim 8 wherein said tread rubber composition is sulfur cured.

20. The tire of claim 9 wherein said tread rubber composition is sulfur cured.

21. The tire of claim 1 wherein said traction promoting resin is comprised of said styrene-alphamethylstyrene resin.

22. The tire of claim 21 wherein said styrene-alphamethylstyrene resin has a styrene content in a range of from about 10 to about 90 percent.

23. The tire of claim 1 wherein said traction promoting resin is comprised of said terpene-phenol resin where said terpene-phenol resin is comprised of a copolymer of phenolic monomer with a terpene comprised of at least one of limonene and pinene.

Description

EXAMPLE I

[0051] In this example, exemplary rubber compositions for a tire tread were prepared for evaluation for use to promote a combination of wet traction and cold weather (winter) performance.

[0052] A control rubber composition was prepared identified as rubber Sample A and experimental rubber compositions identified as rubber Samples B through E were prepared as precipitated silica reinforced rubber compositions containing synthetic elastomers as a combination of styrene/butadiene rubber having an intermediate Tg of about −60° C. and a cis 1,4-polybutadiene rubber having a low Tg of about −106° C. together with traction resin and silica coupler for the precipitated silica.

[0053] The rubber compositions are illustrated in the following Table 1.

TABLE-US-00001 TABLE 1 Parts by Weight (phr) Material Cntrl A Exp B Exp C Exp D Exp. E Non-Productive Mixing (NP) Cis 1,4-polybutdiene 25 25 25 25 25 rubber.sup.1 Styrene/butadiene 75 75 75 75 75 rubber.sup.2 Traction resin A.sup.3 36 36 36 0 0 Traction resin B.sup.4 0 0 0 37 0 Traction resin C.sup.5 0 0 0 0 47 Rubber processing oil.sup.6 26 15 23 23 16 Precipitated silica X.sup.7 140 0 0 0 0 Precipitated silica Y.sup.8 0 140 160 160 160 Silica coupler.sup.9 8.8 6.3 7.2 7.2 7.2 Fatty acids.sup.10 5 5 5 5 5 Carbon black (N330) 1 1 1 1 1 Wax (paraffinic and 1.5 1.5 1.5 1.5 1.5 microcrystalline) Antioxidant(s) 5 5 5 5 5 Zinc oxide 2.5 2.5 2.5 2.5 2.5 Productive Mixing (P) Sulfur 1.2 1.5 1.5 1.5 1.2 Sulfur cure accelerators.sup.11 5.5 3.8 4.4 4.7 5.1 .sup.1High cis 1,4-polybutadiene rubber as Budene1229 ™ from The Goodyear Tire & Rubber Company having a Tg of about −106° C. having a vinyl 1,2-content of less than about 4 percent and a cis 1,4-content of more than about 96 percent .sup.2Styrene/butadiene rubber (SSBR) prepared by organic solution prepared polymerization of styrene and 1,3-butadiene monomers having a styrene content of about 15 percent and a vinyl 1,2-content of about 30 percent (based on the polybutadiene portion of the SSBR) with a Tg of about −60° C. obtained as Sprintan SLR 3402 ™ from Trinseo. The SSBR was a functionalized SSBR end functionalized with functional groups understood to be comprised of alkoxy and thiol groups. .sup.3Traction resin A as copolymer of styrene and alphamethylstyrene (styrene-alphamethylstyrene copolymer) having a softening point of about 80° C. to about 90° C. obtained as Sylvares SA85 ™ from Arizona Chemicals .sup.4Traction resin B as copolymer of styrene and alphamethylstyrene (styrene-alphamethylstyrene copolymer) having a softening point of about 110° C. to 130° C. obtained as Norsolene W120 ™ from Total Petrochemicals .sup.5Traction resin C as copolymer of terpene and phenol having a softening point of about 140° C. to 150° C. obtained as YS Polyster T145 ™ from Yasuhara Chemical .sup.6Rubber processing oil as a TDAE type petroleum based oil .sup.7Precipitated silica X as HiSil315G-D ™ from PPG having a BET (nitrogen) surface area of about 125 m.sup.2/g .sup.8Precipitated silica Y as EZ090G-D ™ from PPG having a BET (nitrogen) surface area of about 90 m.sup.2/g .sup.9Silica coupler comprised of a bis(3-triethoxysilylpropyl) polysulfide containing an average in a range of from about 2 to about 2.6 connecting sulfur atoms in its polysulfidic bridge as Si266 ™ from Evonik .sup.10Fatty acids comprised of stearic, palmitic and oleic acids .sup.11Sulfur cure accelerators as sulfenamide primary accelerator and diphenylguanidine secondary accelerator

[0054] The rubber Samples were prepared by blending the ingredients, other than the sulfur curatives, in a first non-productive mixing stage (NP1) in an internal rubber mixer for about 4 minutes to a temperature of about 160° C. The resulting mixtures were subsequently individually mixed in a second sequential non-productive mixing stage (NP2) in an internal rubber mixer to a temperature of about 140° C. The rubber compositions were subsequently mixed in a productive mixing stage (P) in an internal rubber mixer with the sulfur curatives comprised of the sulfur and sulfur cure accelerators for about 2 minutes to a temperature of about 115° C. The rubber compositions were each removed from the internal mixer after each mixing step and cooled to below 40° C. between each individual non-productive mixing stage and before the final productive mixing stage.

[0055] The following Table 2 illustrates various physical properties of rubber compositions based upon the basic formulation of Table 1 and reported herein as Control rubber Sample A and Experimental rubber Samples B through E. Where cured rubber samples are reported, such as for the stress-strain, hot rebound and hardness values, the rubber samples were cured for about 10 minutes at a temperature of about 170° C.

[0056] For the predictive wet traction, a tangent delta (tan delta) test was run at −10° C.

[0057] For the predictive low temperature (winter snow) performance, the rubber's stiffness test (storage modulus G′) was run at −20° C. to provide a stiffness value of the compounds (rubber compositions) at lower operating temperatures.

TABLE-US-00002 TABLE 2 Parts by Weight (phr) Materials Cntrl A Exp B Exp C Exp D Exp E Traction resin A 36 36 36 0 0 Traction resin B 0 0 0 37 0 Traction resin C 0 0 0 0 47 Precipitated silica X 140 0 0 0 0 Precipitated silica Y 0 140 160 160 160 Properties Cold Weather (Winter) Performance (Stiffness) Laboratory Prediction Storage modulus (G′), 17 11 15 14 16 (MPa) at −20° C., 7.8 Hertz, 1.5% strain (lower stiffness values are better) Wet Traction Laboratory Prediction Tan delta, (−10° C.) 0.54 0.48 0.53 0.55 0.63 (higher values are better) Additional properties Tensile strength (MPa) 15 12 11 12 12 Elongation at break (%) 529 462 479 475 508 Modulus (ring) 300% 7.6 7.8 7.3 8 7.1 (MPa) Shore A hardness 61 60 60 60 60 (100° C.) Storage modulus G′, 2.8 2.2 2.7 2.3 2.1 (MPa) at 100° C., and 1% strain Rolling Resistance Predictive Property Tan delta, 50° C. 0.27 0.19 0.22 0.27 0.26 (lower is better)

Observations from Table 2

Wet Traction—Tan Delta (−10° C.) and Cold Weather Performance—G′ (−20° C.) Considerations

[0058] (A) Use of Precipitated Silica of Lower Surface Area

[0059] Experimental rubber Samples B and C used the same levels of the same traction resin (styrene-alphamethylstyrene copolymer) as Control rubber Sample A, although a precipitated silica having a substantially lower surface area was used (BET nitrogen surface area of 90 instead of a BET surface area of 125 m.sup.2/g for the precipitated silica of Control rubber Sample A).

[0060] Rolling resistance prediction property for a tire with tread of the respective rubber compositions (evidenced by the tan delta at 50° C.) was beneficially improved or maintained in a sense that the tan delta values were beneficially reduced for Experiment rubber Samples B and C and maintained for Experimental rubber Samples D and E.

[0061] Simultaneously, winter (low temperature) properties for Experimental rubber Samples B and C were improved (while also improving the aforesaid predictive rolling resistance) as evidenced by desirably reduced storage moduli G′ at −20° C.

[0062] However, wet traction predictive properties for Experimental rubber Samples B and C were reduced in a sense that the tan delta at −10° C. values were undesirably reduced as compared to Control rubber Sample A.

[0063] (B) Use of Traction Resins with Higher Softening Points

[0064] Experimental rubber Samples D and E used the same lower surface area precipitated silica as Experimental rubber Samples B and C (BET nitrogen surface area of 90 instead of a BET surface area of 125 m.sup.2/g for the precipitated silica of Control rubber Sample A).

[0065] However, Experimental rubber Samples D and E both used significantly higher softening point traction resins (120° C. and 145° C., respectively) than the traction resin used for rubber Sample A and for Experimental rubber Samples B and C having a substantially lower softening point of 85° C.

[0066] In particular, Experimental rubber Sample D used a styrene-alphamethylstyrene copolymer having a softening point of 120° C. and Experimental rubber Sample E used a terpene/phenol copolymer having a softening point of 145° C.

[0067] It is concluded that Experimental rubber Samples D and E, with a combination of high levels of low surface area precipitated silica together with high softening point traction promoting resins, provided better wet traction properties as compared to Control rubber Sample A. Simultaneously, an unpredicted and therefore discovered, predictive improvement in winter (low temperature) properties of Experimental rubber Samples D and E are obtained over the Control rubber sample A.

[0068] It is further concluded that the rolling resistance predictive property of Experimental rubber Samples D and E are beneficially maintained compared to the Control rubber Sample A.

[0069] While certain representative embodiments and details have been shown for the purpose of illustrating the invention, it will be apparent to those skilled in this art that various changes and modifications may be made therein without departing from the spirit or scope of the invention.